RewindBuffer: Fix how log is defined
RewindBuffer: Fix how log is defined

We can only get log from opts if it isn't defined, since we could be subclassed
and it could already exist.

SCPR/StreamMachine,cdgraff/StreamMachine,pteich/StreamMachine,SCPR/StreamMachine,cdgraff/StreamMachine,StreamMachine/StreamMachine,DreamNetwork/StreamMachine,pteich/StreamMachine,DreamNetwork/StreamMachine,pedropapa/StreamMachine,StreamMachine/StreamMachine,pedropapa/StreamMachine